Wireless communication systems are widely deployed to provide various types of communication content, such as voice, data, and so on. Typical wireless communication systems are multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). One class of such multiple-access systems is generally referred to as wireless location area networks (WLANs), such as “Wi-Fi,” and includes different members of the Institute of Electrical and Electronics Engineers (IEEE) 802.11 wireless protocol family. Generally, a Wi-Fi communication system can simultaneously support communication for multiple wireless devices, such as wireless stations (STAs). Each STA communicates with one or more access points (APs) via transmissions on the downlink and the uplink. The downlink (DL) refers to the communication link from the APs to the STAs, and the uplink (UL) refers to the communication link from the STAs to the APs.
Modern navigation systems have typically used satellite-based global positioning system (GPS) for position determination. However, the recent proliferation of WLAN (e.g., Wi-Fi) access points has made it possible for navigation systems to use these access points for position determination, especially in urban areas where there is usually large concentration of WLAN access points. WLAN navigation systems can be advantageous over GPS navigation systems because of limitations of GPS signal coverage. For example, while GPS signals may not be readily available inside a shopping mall, wireless signals generated by WLAN access points inside the shopping mall would be more readily detectable by a STA.
More specifically, for WLAN navigation systems, the locations of the WLAN access points are used as reference points from which well-known trilateration techniques can determine the location (e.g., absolute location and/or relative location) of a wireless device (e.g., a Wi-Fi-enabled cell phone, laptop, or tablet computer). The wireless device can use the round trip time (RTT) of signals transmitted to and from the access points to calculate the distances between the wireless device and the access points. Once these distances are calculated, the location of the wireless device can be estimated using trilateration techniques.
Conventional RTT techniques used to determine the distances between the wireless device and WLAN access points, are typically performed based on a peer-to-peer messaging protocol. Thus, the wireless device needs to know which APs are in proximity to the wireless device in order to exchange peer-to-peer messages in these conventional RTT techniques. For example, the wireless device typically first performs a discovery scan to determine which APs are present on each channel of the WLAN. Alternatively, some location/venue specific databases may be used to determine the APs in the proximity of the wireless device. Once the wireless device has knowledge of which APs are present and on which channels, the wireless device then exchanges messages with each known AP, performing RTT measurements, one AP at a time. However, as WLAN positioning solutions require more and more precision, the wireless device may be required to perform more frequent RTT measurements, with many access points in its vicinity. This high periodicity of discovery scans and many peer-to-peer RTT measurements can cause several problems in the WLAN. For example, current 802.11 connectivity solutions are not designed for such high periodicity solutions, because each discovery scan and RTT measurement is a disruption to the high speed data capabilities of the WLAN. In addition, the increased periodicity of discovery scans and peer-to-peer RTT measurements can adversely increase the power consumption of the wireless device. Additionally, in the scenarios where there are many mobile devices doing similar operations (for example in crowded stadiums, where many mobile devices may be concurrently trying to perform Location Based Services), the RTT Requests from many mobile devices may collide with one another, making the WLAN connectivity problems worse.